1. Field of the Invention
The present invention relates to a carriage arm assembly for a magnetic disk drive, in particular to a structure of a carriage arm assembly which is suitable for positioning a magnetic head.
2. Description of the Prior Art
Recently, in the field of a magnetic disk drive, it has been required to improve recording density in order to increase recording capacity. For this purpose, it is important to improve accuracy of positioning a magnetic head. However, as inhibition factors from improving the positioning accuracy, there are raised a positioning error due to vibration of a mechanism system resulting from rotation of a disk or from operation of positioning a carriage arm assembly, and a positioning error due to vibration added from the outside of the magnetic disk drive. In order to reduce these positioning errors, it is necessary to widen a servo band width in positioning-control, or reduce the vibration of the mechanism system.
Among these, the vibration of the mechanism system due to the operation of positioning the carriage arm assembly is mainly composed of a vibration component resulting from excitation of each part of the carriage arm assembly caused by a driving force input thereto when positioning the head to a target track during operation of moving the head from a track to another track.
Especially, a vibration mode in which in-plane bending and out-plane bending of a carriage arm (hereinafter referred to as simply “arm”) are generated has a significant influence on the positioning accuracy because the head disposed at a tip end of the arm is swung in the case of a swing-type carriage arm assembly.
Further, also in a condition in which the head follows its target track after the head moves to the target track, a vibration component resulting from excitation of each part of the arm due to turbulence generated by rotation of a disk also has an influence on the positioning accuracy. Particularly, a primary vibration component of the in-plane bending of the arm is often generated at a frequency between several hundred Hz and 1 kHz, which may cause a problem.
Herein, a primary mode of the in-plane bending of the arm and a primary mode of the out-plane bending of the arm refer to a mode in which each of a plurality of arms deforms in the same manner as a primary bending of a cantilever, and a secondary mode of the in-plane bending of the arm and a secondary mode of the out-plane bending of the arm refer to a mode in which each of the plurality of arms deforms in the same manner as a secondary bending of the cantilever.
Further, there is a problem that a read/write speed of the disk drive is reduced because a time until reading-out or writing-in of data become possible is increased due to residual vibration in the positioning operation.
As a method for reducing the residual vibration, there has been raised a method of reducing the vibration by using a viscoelastic material as described in JP-A-4-168671.
According to the method, there is provided a structure in which at least a pair of spring means are provided, of which one end is fixed to a body and of which another end applies a spring force via the viscoelastic material to the arm. By this structure, a relative displacement is generated between the arm and a plate spring in the vibration mode in which the out-plane bending of the arm is generated, so that a strain is generated in the viscoelastic material placed between the arm and the plate spring to damp the vibration of the arms.
According to a method disclosed in JP-A-4-168671, although a damping effect due to the strain in the viscoelastic material can be expected for the vibration mode in which the out-plane bending of the arm is generated, there is a problem, in the vibration mode in which the in-plane bending of the arm is generated, that the arm, the viscoelastic material, and the plate spring are integrally vibrated because a direction of displacement of the arm corresponds to a direction toward which the plate spring are urged, so that the strain is not generated in the viscoelastic material and therefore no damping effect is obtained.
In addition, there is also considered a problem that the arm is deformed due to a structure in which the arm is urged from a side thereof by the plate spring. Considering the case that the arm is pushed by the plate spring only from one side of the arm, off-track may occur with time, and a distance between heads may change and increase in comparison with an initial state, particular in the case of a rotary actuator system. Further, in this case, it is considered that imbalance in rigidity of the arm occurs so that the out-plane vibration is readily observed in a disk radial direction. Thus, it is necessary to provide the above described plate springs on both sides of the arm, and the plate springs are required to have a spring structure so as to cover a wide area in a side surface of the carriage arm assembly, therefore a relatively large degree of increase in weight with respect to the weight of the entire carriage is required. As a result, it is considered that new problems need to be solved, such as narrowing of a servo band width due to deterioration in access time or reduction of a main resonant frequency.
In this application, in order to solve the above described problems, it is an object of the present invention to provide a magnetic disk drive which has a large recording capacity by reducing residual vibration in operation of positioning a head and vibration due to disk rotation wind turbulence when the head follows its target track to improve positioning accuracy and thereby improve recording density. Further, there is provided a structure of a carriage arm assembly of the magnetic disk drive which enables high speed transfer by reducing a positioning error to improve a read/write speed.